1. The Field of the Invention
The present invention relates to systems and methods for controlling ink delivery to print heads in a printing system. More particularly, the present invention relates to systems and methods for adjusting a pressure of ink at the nozzles of the print heads using temperature data of the printing system.
2. The Relevant Technology
Printing systems, such as ink-jet printing systems, are well known devices and are available from various manufacturers. A typical ink-jet printing system includes multiple print heads mounted on a movable carriage. Each print head usually has multiple nozzles through which ink is delivered during a printing process. As the carriage moves back and forth across a media, ink is deposited on the media by the nozzles of the print heads at appropriate times and at precise locations. In typical color printing processes, there is a print head for each color and each color may be deposited on the media during each pass of the print head.
The nozzles on each print head must be controlled to deposit ink drops in precise locations. The relative placement of ink drops of different colors is also controlled by the printing system. As the ink drops are ejected from the nozzles and placed on the media, it is often desirable to ensure that all of the deposited ink drops have the same volume. Of course, there are instances where different amounts of ink may be deposited in a given process. However, the amount of ink deposited on a media during a printing process can have an impact on the quality of the image. Excessive ink may result in smearing or ink running on the media, thereby reducing the image quality, while insufficient amounts of ink may result in a poor image or visible lines in the image.
Part of the problem in delivering a proper volume of ink to a media is related to the nozzle itself and to the meniscus of ink associated with each nozzle. Each nozzle of a print head is associated with its own meniscus and when the meniscus extends beyond its own boundaries and encroaches on the meniscus of a neighboring nozzle, the meniscuses merge. When this occurs, the amount of ink delivered to the media can no longer be effectively controlled and excessive ink is often delivered to the media. When the meniscuses merge, the ink can also solidify on the print head and prevent ink from being deposited by the affected nozzles. The amount of ink delivered to the media is reduced in this case and the quality of the printed image is again reduced.
Furthermore, when a curvature of the meniscus exceeds certain limits governed by the surface tension characteristics of the ink and the adhesion of the ink to the nozzle, the meniscus can break. When the meniscus breaks, ink “drools” from the nozzle before, during, and after a printing process and reduces the quality of the printed image. In addition, the quality of the printed image can also be affected when the meniscus becomes concave and extends inwardly through the nozzle and into the print head. When this occurs, insufficient ink is delivered to the media.
Many attempts have been made to control the volume of ink deposited from the print nozzles. Further, many attempts have been made to control the curvature of the meniscus of the ink at the nozzles to prevent insufficient or excessive amounts of ink from being deposited upon printable media during a printing process.
In numerous ink-jet printers, ink is delivered to each print head by a tube that connects the print head to an ink reservoir positioned above the vertical level of the print head. During the printing process, ink flows along the tube to the nozzle of the print head under the force of gravity as the weight of the ink within the ink reservoir forces the ink stored in the tubing toward the nozzles. The volume of ink forced to each nozzle depends upon the particular volume of ink stored in the ink reservoir, fluid dynamic characteristics of the tubing, and chemical characteristics or properties of the ink. For instance, when an ink having a high absolute viscosity is employed with a printing device, a low volume of ink is forced to a nozzle under a given pressure. Similarly, when an ink having a low absolute viscosity is employed with a printing device, a high volume of ink is forced to a nozzle under the same given pressure. Changes to the chemical composition of the ink causes changes in the effectiveness of these gravity-type ink-jet printers. These types of ink-jet printers are difficult to use with a variety of different inks because of the effect that the given pressure has on the volume of ink deposited on the media.
Other ink jet printers utilize a surge suppressor to pressurize the ink as it is passed into the ink reservoir. The surge suppressor maintains an average pressure within the tube connecting the ink reservoir with the print head. Typically, the surge suppressor used in such ink-jet printers is designed for a particular ink, with associated characteristics and properties. Additionally, surge suppressors are typically not adjustable and allow large ranges of pressure fluctuations.
The ability to deliver a volume of ink through a nozzle is also affected by the temperature of the ink and of the printing system. The temperature of a print head can increase quickly when printing and change the temperature of the ink, which has an effect on the viscosity of the ink. The printing system can also generate heat that has an impact on the pressure of the ink. The curing units of ultraviolet (UV) ink-jet printers or the infrared (IR) units of other ink-jet printers, for example, can generate significant amounts of heat that can adversely affect the volume of ink delivered to a media by altering the viscosity of the ink. Because the viscosity of the ink changes with temperature, the pressure applied to the ink is no longer correct and may result in excessive or insufficient quantities of ink being delivered through the nozzles of the print heads.
Changes in the viscosity of the ink due to temperature can have an impact on the quality of the printed image. The change in viscosity means that the pressure applied to the ink is no longer correct and may cause a meniscus to rupture or to merge with other meniscuses. In each case the quality of the printed image is reduced. Existing systems do not adjust the pressure of the ink relative to the current temperature. It would be an advance in the art to provide systems and methods that maintain high quality image reproduction through control of the volume of ink deposited from a nozzle of a print head and more particularly to systems and methods for controlling the pressure of ink relative to at least the temperature of the ink or of the printing system.